Variadic tuple assignment fail

[craigphicks]

Bug Report

🔎 Search Terms

variadic tuple bug

🕗 Version & Regression Information

The same behavior is visible from 4.2.3 through 4.8dev
although it it as only been a bug since variadic tuples.

⏯ Playground Link

Playground link with relevant code

💻 Code

// These should be OK since variadic tuples (rest can go anywhere)
// versions 4.2.3 ~ 4.8 dev.
{
    type T12 = ["^", ...(string | boolean | undefined)[], "$"]
    const t12a:T12 = ["^", "$"];        // Should not be an error
    const t12b:T12 = ["^", true, "$"];  // Should not be an error
}

🙁 Actual behavior

As shown.

🙂 Expected behavior

Not errors, because a match exists.

Additional Info

I examined the code. checkArrayLiteral in checker.ts performs a unidirection (left to right) search only,

However, the output from createNormalizedTupleType outputs a normalized type that can have a single tuple in the middle (like the one in the example).

That requires a bidirectional search to get the right results.

Alternatively, createNormalizedTupleType could be forced to roll up everything after the first rest into a single rest. But such an algorithm would result in more false postives (false passes) than necessary. So a bidirectional search is preferable.

I can provide more details if necessary. (I even have bi-directional search code that passes all the baselines tests). Just ask if you want it.

[Andarist]

note from my issues scavenger hunt: this issue was extracted from #49105 and the draft PR here seems to implement a fix for this

[craigphicks]

Seems to have been fixed in 5.0.4

[Andarist]

This was fixed between 5.0.0-dev.20230218 and 5.0.0-dev.20230219, so likely by #52769

[craigphicks]

@Andarist - Thank you very much for finding that!